With the higher and higher request of the user for radio access rate, Wireless Local Area Network (WLAN) emerges as the times require, which can provide high-rate radio data access in a very small area. WLAN comprises various different techniques and the technical standard IEEE 802.1b is widely applied at present, which adopts 2.4 GHz frequency channel and the highest data transmission rate of 802.1b is 11 Mbps, therein IEEE 802.11g and Bluetooth technique also adopts this frequency channel, and the highest data transmission rate of 802.11g is 54 Mbps. Other new techniques like IEEE 802.11a and ETSI BRAN Hiperlan2 also adopt 5 GHz frequency channel and the highest transmission rate can be 54 Mbps.
Despite the various different radio access techniques, most of WLAN are used to transmit Internet Protocol (IP) packet data. As to a radio IP network, the adopted specific WLAN technique is generally transparent to the upper IP layer. The basic structure thereof is to utilize Access Point (AP) to fulfill user terminal's radio access and establish an IP transmission network through network control and connection equipment.
With the emergence and development of WLAN technique, interworking between WLAN and various radio mobile communication networks, like Global System for Mobile Communications (GSM), Code Division Multiple Access (CDMA) system, Wideband CDMA (WCDMA) system, Time Division-Synchronous CDMA (TD-SCDMA) system and CDMA 2000 system, is becoming the focus of current research. These kinds of networks are also called interworking networks, e.g. WLAN-3G interworking network. The present invention is more suitable for, but not limited to, these interworking networks. In the 3rd Generation Partner Project (3GPP) Organization for Standardization, user terminal can be connected with the Internet or Intranet through WLAN-AN, and can also be connected with a user's home network of 3GPP system or a visited network of 3GPP system through WLAN Access Network (WLAN-AN), specifically speaking, the WLAN user terminal is connected to a 3GPP home network through WLAN-AN when being locally accessed, namely, connected to a Home Public Land Mobile Network (HPLMN), as shown in FIG. 2; when the user terminal is roaming, it is connected with 3GPP visited network, namely a Visited Public Land Mobile Network (VPLMN), through WLAN-AN, and part of the entities in 3GPP visited network are respectively connected to corresponding entities in 3GPP home network, for instance, the 3GPP Authentication Authorization Accounting (AAA) proxy in 3GPP visited network and 3GPP Authentication Authorization Accounting (AAA) server in 3GPP home network; WLAN Access Gateway (WAG) in 3GPP visited network and Packet Data Gateway (PDG) in 3GPP home network, etc, as shown in FIG. 1. Thereby, FIG. 1 and FIG. 2 are schematic diagrams illustrating the framework for intercommunication between WLAN system and 3GPP system in the case of roaming and non-roaming respectively.
With the reference to FIG. 1 and FIG. 2, a 3GPP system mainly comprises Home Subscriber Server (HSS)/Home Location Register (HLR), 3GPP AAA server, 3GPP AAA proxy, WAG, PDG, Charging Gateway (CGw)/Charging Collection Function (CCF) and Online Charging System. User terminal, WLAN-AN and all entities of 3GPP system jointly constitute a 3GPP-WLAN interworking network, which can be taken as a WLAN service system. Thereby, 3GPP AAA server takes charge of authentication, authorization and accounting upon the user, collecting and transferring the charging information from WLAN-AN to charging system; PDG takes charge of transmitting the user data from WLAN-AN to 3GPP network or other packet networks, or vice versa; charging system is mainly in charge of receiving and recording user's charging information from the network, and OCS is in charge of instructing the network to periodically transmit online charging information according to charging situation of online charged user, as well as in charge of statistics and control.
In the case of non-roaming, when a WLAN user terminal expects to be directly accessed to Internet/Intranet, after finishing access authentication and authorization with AAA server (AS) through WLAN-AN, the user terminal can be accessed to Internet/Intranet through WLAN-AN. If the user terminal also expects to access 3GPP Packet Switch (PS) domain service, the user terminal can further apply to 3GPP home network for Scenario3 service, namely: WLAN user terminal requests AS of 3GPP home network for Scenario3 service authorization, AS of 3GPP home network performs service authentication and authorization upon this service authorization request, if successful, AS will send an access accept message to user terminal and allocate corresponding PDG for user terminal, the user terminal can access 3GPP PS domain service after the channel between user terminal and the allocated PDG is established. Meanwhile, according to network utilization situation of the user terminal, CGw/CCF and OCS records charging information. In case of roaming, when a WLAN user terminal expects to be directly accessed to Internet/Intranet, the user terminal can apply to 3GPP home network for accessing the Internet/Intranet through 3GPP visited network. If the user terminal also expects to further apply for Scenario 3 service and access 3GPP Packet Switch (PS) domain service, the user terminal needs to initiate a service authorization procedure towards 3GPP home network through 3GPP visited network, wherein the procedure thereof is also performed between user terminal and AS of 3GPP home network, if the authorization is successful, AS will allocate corresponding home PDG for the user terminal, and the user terminal can access 3GPP PS domain service after the channel between user terminal and the allocated PDG is established.
In a 3GPP-WLAN interworking network, if a WLAN is connected to a plurality of 3GPP visited networks at the same time, namely a plurality of mobile communication operational networks, the WLAN user terminal will have to select a desirable mobile communication operational network to access and the two schemes thereof are as shown in FIG. 3 and FIG. 4. Therein, FIG. 3 is a flowchart illustrating the successful procedure of the user terminal directly selecting a mobile communication operational network to access, comprising:
Step 301˜303: after the radio connection between WLAN user terminal and WLAN-AN is established, the network, e.g. WLAN-3G network, or WLAN user terminal initiates the access authentication procedure, and WLAN-AN sends user identity request message to this WLAN user terminal; after receiving the request message, the WLAN user terminal returns a user identity response message with network selection information to the WLAN-AN. Hereby, the network selection information is information of the mobile communication operational network that the user terminal is accessing and to which WLAN network is connected; the access authentication procedure between WLAN-AN and user terminal is an Extendable Authentication Protocol (EAP) procedure. Generally, network selection information is contained in a user identifier field defined in Network Access Identifier (NAI) format.
Step 304˜306: after receiving the message returned by user terminal, WLAN-AN judges whether the network selection information in the message belongs to the mobile communication operational network to which WLAN network is currently connected, if yes, WLAN-AN will determine the 3GPP AAA Proxy or 3GPP AAA Server of the mobile communication operational network selected by this user terminal, and then send user identifier and access authentication request to the 3GPP AAA Proxy or 3GPP AAA Server, so that 3GPP AAA Proxy or 3GPP AAA Server can authenticate and authorize the user, if the user passes the authentication and authorization, the subsequent access procedure will be executed.
FIG. 4 is a flowchart illustrating the procedure of user terminal re-selecting a mobile communication operational network to access when the initial selection is failed, comprising:
Step 401˜403: completely the same as step 301˜step 303.
Step 404˜405: after receiving the message returned by user terminal, WLAN-AN detects that the network selection information in the message does not belong to the mobile communication operational network to which WLAN network is currently connected, and then sends a network advertisement message containing all mobile communication operational networks to which the WLAN-AN is connected.
Step 406˜407: after receiving the network advertisement message, user terminal re-selects a mobile communication operational network to access according to information of the mobile communication operational network indicated in the advertisement message, and then sends a user identity response message with new network selection information to WLAN-AN.
Step 408˜409: completely the same as step 305˜306.
It can be seen from the above scheme that, well-established procedure of the user terminal selecting an access network already exists in 3GPP-WLAN intercommunication network, however, when a certain WLAN-AN is connected to a plurality of VPLMN networks, after certain user terminal is connected to one VPLMN network thereof through this WLAN-AN, if this user terminal need to disconnect from current connected VPLMN network and re-select another VPLMN network connected to this WLAN-AN because of charging or visited service scope or other reasons, there is no specific solving scheme put forward for this situation yet.